show view preview option. We also now start the rename task during preview and
use its result during apply. Also update unit tests.

changed preview warning tagger name from "Warning" to "Preview Warning" to reduce confusion between compiler warning tag.

Fixes #540 "Stale rename entries in the lightbulb menu"

Prior to this change, dismissed rename tracking sessions continued to
provide codefixes which would silently fail when invoked, without
completing the rename operation.

With this change, we now do the following when rename tracking is
manually dismissed:

- Trigger the diagnostic service to reanalyze the document, thus
removing the rename tracking diagnostic.
- Stop providing a codefix when requested
- Show a dialog if a cached codefix is invoked explaining that the
rename was not performed.

Here are the there user scenarios:

1. The user dismisses rename tracking

    - The lightbulb will continue to show in the margin, regardless of
whether any codefix/refactoring is actually still available.

2. The user expands the lightbulb without it ever having been expanded
before.

    - In this case, we are queried for fixes and will not return any, so
either the lightbulb will disappear or it will contain other relevant
codefixes/refactorings at that position, excluding rename.

3. The user expands the lightbulb after it was previously expanded.

    - Our fix was already cached, so we can only give a reasonable message
when it is invoked.

Once #885 is fixed, we can instead implement IDiagnosticUpdateSource and
avoid forcing diagnostic reanalysis.

Fixes #466 "Use a 'TriggerDiagnosticDescriptor' for the rename tracking
diagnostic"

Updates the RenameTrackingDiagnosticAnalyzer to use a
TriggerDiagnosticDescriptor, which prevents the diagnostic title from
appearing in the preview area of the lightbulb. We now pass the
RenameFrom and RenameTo names as part of the Diagnostic's property bag
and construct the localized codefix title based on these in the codefix
itself.

Fix #554: This fixes a crash that was caused by invoking a lightbulb
item that caused an Inline Rename session to launch when there's already
an inline rename session active. We now check for inline rename sessions
during lightbulb commit. If an inline rename session is active, we halt
the lightbulb commit and tell the user to complete their rename session.

This only prevents one (but probably the most frequent) manifestation of
a larger problem in which rename is trying to perform a series of
changes to the workspace that can be interrupted by some other feature
applying its changes to the workspace. This larger design problem is
tracked as #681.